It is fairly well established that many pathological conditions, such as infections, cancer, autoimmune disorders, etc., are characterized by the inappropriate expression of certain molecules. These molecules thus serve as "markers" for a particular pathological or abnormal condition. Apart from their use as diagnostic "targets", i.e., materials to be identified to diagnose these abnormal conditions, the molecules serve as reagents which can be used to generate diagnostic and/or therapeutic agents. A by no means limiting example of this is the use of cancer markers to produce antibodies specific to a particular marker. Yet another non-limiting example is the use of a peptide which complexes with an MHC molecule, to generate cytolytic T cells against abnormal cells.
Preparation of such materials, of course, presupposes a source of the reagents used to generate these. Purification from cells is one laborious, far from sure method of doing so. Another preferred method is the isolation of nucleic acid molecules which encode a particular marker, followed by the use of the isolated encoding molecule to express the desired molecule.
To date, two strategies have been employed for the detection of such antigens in, e.g., human tumors. These will be referred to as the genetic approach and the biochemical approach. The genetic approach is exemplified by, e.g., dePlaen et al., Proc. Natl. Acad. Sci. USA 85: 2275 (1988), incorporated by reference. In this approach, several hundred pools of plasmids of a cDNA library obtained from a tumor are transfected into recipient cells, such as COS cells, or into antigen-negative variants of tumor cell lines which are tested for the expression of the specific antigen. The biochemical approach, exemplified by, e.g., Falk et al., Nature 351: 290 (1991), and Kawakami et al., Nature 369: 69 (1994) both of which are incorporated by reference, is based on acidic elution of peptides which have bound to MHC-I molecules of tumor cells, followed by reversed-phase high performance liquid chromotogaphy (HPLC). Antigenic peptides are identified after they bind to empty MHC-I molecules of mutant cell lines, defective in antigen processing, and induction of specific reactions in cytolytic T-lymphocytes. These reactions include induction of CTL proliferation, TNF release, and lysis of target cells, measurable in an MTT assay, or a .sup.51 Cr release assay.
These two approaches to the molecular definition of antigens have the following disadvantages: first, they are enormously cumbersome, time-consuming and expensive; second, they depend on the establishment of cytolytic T cell lines (CTLs) with predefined specificity; third, their relevance in vivo for the course of the pathology or disease in question has not been proven, as the respective CTLs can be obtained not only from patients with the respective disease, but also from healthy individuals, depending on their T cell repertoire.
The problems inherent to the two known approaches for the identification and molecular definition of antigens is best demonstrated by the fact that both methods have, so far, succeeded in defining only very few new antigens in human tumors. See, e.g., van der Bruggen et al., Science 254: 1643-1647 (1991); Brichard et. al., J. Exp. Med. 178: 489-495 (1993); Coulie, et al., J. Exp. Med. 180: 35-42 (1994), Kawakami et al., Proc. Natl. Acad. Sci. USA 91: 3515-3519 (1994).
It would be desirable to have available a method which can be used not only for detection of tumor-associated antigens, but to determine molecules associated with any abnormal or pathological condition. Such a method would also facilitate the identification of such molecules, thereby enabling their use on the generation of, e.g., antibodies, cytolytic T cells, and so forth.
It is therefore the purpose of the present invention to develop a method for the simple detection and molecular characterization of antigens in human tissues, especially in tumor cells, which are useful -in the molecular diagnosis of diseases and/or for immunotherapy and gene therapy of infectious, autoimmune and malignant diseases. The invention is delineated in the disclosure which follows.